Glossary

A

A substance that enhances the immune response to the antigen with which is it mixed

Antibiotic

A compound that inhibits the growth and reproduction of bacteria. Antibiotics are not effective against viruses.

Antibody

A specialized protein produced by the immune system that helps destroy disease-causing organisms. An antibody is a component of humoral immunity. Antibodies can be effective defenders against both bacteria and viruses. An antibody must be made specifically for each pathogen.

Antigen

A protein or other substance capable of triggering an immune response

Antiviral

A compound that inhibits the growth and reproduction of viruses

Aptamer

Short strands of DNA or RNA that are designed to bind to certain target molecules

Arthropod

An invertebrate animal that has an external skeleton, a segmented body, and jointed appendages. This classification includes insects, spiders, and crustaceans. Some types, such as mosquitoes and ticks, can transmit diseases.

Attenuate

To reduce the virulence of

B

Bacterium

A class of microorganisms that are made of a single cell with a certain structure. While many bacteria are beneficial, some bacteria can cause disease. (plural, bacteria)

Biologics

A biological product used in medicine

Biosafety level 3 (BSL-3)

A specially designed, high-containment laboratory facility used for work with infectious disease agents that can cause severe disease or are potentially lethal. The Centers for Disease Control and Prevention has established four levels of biosafety laboratory facility, with level 4 designated for use with the most hazardous agents.

Broad-spectrum antibiotic

An antibiotic that is effective against a wide range of bacteria, including both gram-positive and gram-negative bacteria. Examples include ampicillin, amoxicillin, ciprofloxacin, and tetracycline.

C

CD4+ T cell

A cell of the immune system, also known as a “helper” cell, that helps other immune system cells produce antibodies. CD4+ T cells are the cell type that are infected and destroyed by HIV.

Cell

The basic unit of all living things

Cell-mediated immunity

Part of the immune system in which specific immune system cells, such as cytotoxic T cells, directly attack infected cells

Chromosome

One of a segment of DNA that together make up the genetic information of an organism. Humans have 23 pairs of chromosomes.

Clade

A group of organisms that includes all descendants of one common ancestor

Cohort

Group of individuals used in a study that have a statistical factor, such as age, in common

Cytokine

A small protein that is secreted by certain cells of the immune system that plays an important role in cell signalling by affecting the behavior of other cells. Examples include interferon and interleukin.

Cytotoxic T cell

Also known as “killer” T cells, a type of immune system cell that can directly attack infected cells.

D

Disseminate

To disperse or spread about widely

DNA

Deoxyribonucleic acid, the chemical structure that contains the genetic information of an organism. The double helical structure is made of two strands consisting of deoxyribose and phosphate and is held together by bonds between purine and pyrimidine bases which project inward from two chains and form the genetic code.

E

Enteric Infection

A disease of the intestines caused by an infection that is characterized by diarrhea, vomiting, nausea, and abdominal discomfort that may result in significant loss of fluids and electrolytes.

Envelope

A lipid (fatty) covering that surrounds a viral particle. It is derived from the cell membrane of the host cell when the virus buds, or exits, the infected cell. The envelope is important for entry into a host cell. Viruses with an envelope are generally less stable outside of a host than viruses that lack an envelope. Viruses that are enveloped include HIV, influenza, Ebola, dengue, and chikungunya.

Enzyme

A protein that acts as a biological catalyst. Enzymes are necessary to produce chemical reactions within a cell.

Epidemic

A disease affecting a large number of individuals within a population, community, or region at the same time

Epidemiologist

A medical scientist who studies the incidence, distribution, and control of disease in a population

Eradication

The complete elimination of a disease

Eukaryotes

Organisms whose cells possess a membrane-bound structure called a nucleus that contains the genetic material (DNA)

F

Febrile

Having or showing symptoms of a fever

Functional genomics

A field that attempts to describe the functions and interactions of genes and proteins by using genome-wide approaches (as opposed to the classic single gene approach). It combines data from DNA sequencing, gene expression, and protein function to try to understand complex processes that occur within cells.

Fungi

A diverse group of single-celled or multi-cellular eukaryotic organisms that decompose and feed on organic matter. Examples include yeasts, mushrooms, and mold.

G

Gene

A sequence of genetic material that provides the information to make a specific protein.

Genome

The entire genetic information of an organism.

Gram-negative bacteria

A category of bacteria that do not produce a positive result with a violet dye staining technique (bacteria that do appear violet are referred to as gram-positive). Gram-negative bacteria include Escherichia coli, Acinetobacter, Pseudomonas, and Klebsiella.

Gram-positive bacteria

A category of bacteria that produce a positive result with a violet dye staining technique, due to the presence of thick layer of peptidoglycan in their cell walls (bacteria that do not appear violet are referred to as gram-negative). Gram-positive bacteria include the streptococci, staphylococci, and the bacterium that causes anthrax.

H

Heme

A small molecule that consists of an iron atom contained in the center of a large heterocyclic ring called a porphyrin. Heme is involved in many metabolic reactions that occur in the body and is sequestered by specific heme-binding proteins such as hemoglobin.

Humoral immunity

Part of the immune system that provides immunity against disease-causing organisms in body fluids. The main functional unit of humoral immunity is an antibody.

I

Immune response

The body’s immune system response that defends against attacks from disease-causing agents. The body can produce two different immune responses – humoral immunity and cell-mediated immunity.

Immunity

The resistance to an infectious disease agent that can be developed by prior exposure to the pathogen or through vaccination

Immunogen

A substance that produces an immune response

Immunogenicity

The ability of an antigen to elicit an immune response

Immunoreactive

Participating in an immune response, such as by reacting with a specific antibody, as determined by some immunological assay or technique

M

Macrophage

A cell of the immune system that functions as one of the body’s first defenders against disease-causing organisms. Macrophages can engulf and destroy pathogens.

Microbiome

Also known as the microbiota, the collection of microbes that inhabits the body. Microbial cells are estimated to outnumber human cells by a factor of ten to one. The microbiome influences human health and disease.

Microliter

One millionth of a liter

Microorganism

Also called microbe, an organism of microscopic size

MicroRNA

A short piece of single-stranded RNA about 21 to 23 bases in length that regulates the expression of genes. MicroRNAs function by binding to a matching piece of messenger RNA that encodes a protein and decreasing the production of that protein.

Mortality

The number of deaths in a given time or place

Mucosal

Relating to the mucous membranes of the body. These are sites where many important pathogens, such as influenza, enter the body.

N

Nanometer

One billionth of a meter

Negative-sense RNA

Viral RNA with a base sequence complementary to that of messenger RNA (mRNA). The RNA must be converted to positive-sense RNA by a viral enzyme called RNA polymerase before translation into protein can occur. Viruses that have negative-sense RNA genomes include influenza and Ebola.

Neuraminidase

A protein found on the surface of influenza viruses that is needed for the virus to exit the host cell and infect more cells. The action of this protein is inhibited by the class of antiviral drugs that includes the drug Tamiflu®. In the system using for naming influenza subtypes (H1N1, for example), the N stands for neuraminidase.

O

Oligosaccharide

A carbohydrate that is composed of a small number (3 to 10) of simple sugar units linked together.

P

Pandemic

A disease occurring over a wide geographic area and affecting a very high proportion of the population. This term is often used to describe large outbreaks of influenza that occur worldwide and cause a high rate of death.

Pathogen

An organism that can cause disease, such as a bacterium or a virus

Pathogenic

Capable of causing disease

Pathogenesis

The mechanism by which a certain agent causes disease

Peptide

Short chain of linked amino acids. Amino acids are the building blocks of proteins.

Phase I clinical trial

The first stage in testing new drugs or vaccines in humans. Phase I trials are performed on small numbers of people and are designed primarily to test the safety of the new drug and to obtain information about dosages. Drugs that pass phase I trials go on to trials that determine effectiveness and possible side effects and are tested on larger groups of people. If safety and effectiveness are demonstrated, the drugs or vaccines may become approved as treatments.

Placebo

An inert substance used in a controlled experiment to test the efficacy of another substance, such as a drug or a vaccine

Plasmid

A circular segment of DNA that encodes a separate set of genes than those present in chromosomes. Plasmids are most often found in bacteria, but they are also useful to scientists as vectors.

Polymerase chain reaction (PCR)

A technique to amplify a single or few copies of a piece of DNA by several orders of magnitude, generating millions or more copies of a particular DNA sequence

Polypeptide

A chain of amino acids linked together. Amino acids are the building blocks of proteins.

Positive-sense RNA

Viral RNA that has the same base sequence as mRNA which allows it to function as a template for protein synthesis during viral replication

Probiotic

Live microorganisms that are intended to have health benefits. They consist of members of the microbiota that have beneficial effects and may be used to counter the damaging effects of harmful bacteria. For example, they may help prevent diarrhea caused by some infections and antibiotics.

Protein

Components of cells and viruses that play structural and functional roles in cells

R

Reactogenicity

Ability to cause an immunological reaction

Reassortment

The recombination or mixing of the genetic material of viruses; may occur when two different influenza virus strains infect the same cell, resulting in the formation of a new influenza virus strain

Recombinant

Produced by genetic engineering

Recombination

The process by which DNA is broken and genetic material is exchanged through the crossover of DNA between maternal and paternal chromosomes. This can result in offspring having different combinations of genes than their parents.

Retrovirus

A type of virus that uses RNA as its genetic material (rather than DNA). Examples include HIV and HTLV.

RNA

Ribo nucleic acid, a chemical structure that is related to DNA, but has only one strand and a somewhat different chemical composition. RNA performs a variety of functions in the cell and can act as a messenger to carry the genetic code from the DNA to other parts of the cell. RNA can also serve as the genetic material of some viruses.

S

Sepsis

The body's extreme immune response to an infection that causes damage to tissues and organs and can lead to death. Its incidence appears to be increasing, in part due to drug-resistant infections.

Serum

The clear, amber-colored liquid that separates out when blood coagulates. It is protein-rich and contains antibodies.

Single nucleotide polymorphism

Variation in a single base in the genetic code between different individuals of the same species

Spore

A form of a microorganism, such as a bacterium, that is dormant and stable in the environment, but can become capable of reproducing after infecting an animal or person

T

T cell

A type of white blood cell that plays an essential role in the immune system. The "T" stands for thymus which is the organ where the cells mature (as opposed to another type of white blood cell, called B cells, which mature in the bone marrow). Subsets of T cells express different receptors on the surface of the cell and perform specific functions. Also known as a T lymphocyte.

Toxin

A poison that produces illness by affecting bodily functions

Transcription

The process by which the genetic information encoded in DNA is copied into a complementary copy in RNA

V

Vaccination

Injection of a weakened or mild form of a disease-causing agent to produce immunity

Vaccine

A preparation of killed or weakened microorganisms that is administered to produce or increase immunity to a particular disease

Vector

A segment of genetic material that is used as a vehicle to introduce specific genes into cells

Virulence

The ability to cause rapid and severe disease

Virus

A microscopic particle that is made up of genetic material (either DNA or RNA) and protein that can replicate only inside living cells

Virus-like particle

A particle assembled from multiple copies of the capsid protein that, like a virus, can produce an immune response, but unlike a virus, is not infectious because it does not contain genetic material

Z

Zoonosis

A disease that is transmitted from animals to humans. The incidence of zoonoses (plural) increases when humans exist in close contact with animals and when humans encounter animals in new geographical regions.